Radiation detector with an ionizable gas atop an integrated circuit

ABSTRACT

The radiation detector includes tissue equivalent bubbles of plastic defining volumes of gas to be ionized by radiation. One or more integrated circuit (ICs) are disposed below the volumes of gas and a collecting electrode on the IC is in direct contact with the gas. Circuitry for generating an electric field within the volume of gas moves the ions therein to the collecting electrode. The collecting electrode is part of an amplifying circuit disposed within the IC. The output from the amplifier is representative of the collected ions and therefore representative of the radiation. The signal from the amplifier is sent to an interface which conditions, buffers and stores the signal. The radiation dose and dose rate are computed in the interface. A communications section transfers that data from the radiation detector. A separate calibration and display unit calibrates the interface by controlling the conditioning of the signal. An area monitor and air monitor are further enhancements of the radiation detector. The radiation detector includes several circuitry arrangements for minimizing inaccuracies due to leakage currents to the collecting electrode from the amplifying circuit. Such circuitry arrangements include duplicate discharge and amplifying circuits not connected to a functioning collecting electrode; subtracting circuitry for subtracting a signal valued proportional to the leakage current; and a current source inducing current opposite in polarity to the leakage current.

This is a continuation of application Ser. No. 07/007,195, filed Jan.27, 1987, now U.S. Pat. No. 4,804,847.

BACKGROUND OF THE INVENTION

Ionizing radiation presents a direct hazard to people; therefore, themeasurement of radiation in environmental settings is important. Thetype of radiation monitor or detector used to measure the radiationdepends upon the type of radiation, e.g., beta, alpha or X-ray and theenvironmental setting, e.g., an environmentally isolated laboratory, anopen mine, a waste dump holding potentially hazardous material. Thelaboratory most likely requires a monitoring system with a continuousdisplay and singular or multiple radiation detectors; the mine requiresa moderately sensitive portable area detector; and the waste dump arelatively sensitive, directional detector.

D. A. Waechter et al. describe in an article entitled "New GenerationLow Power Radiation Survey Instruments," a standard portable dosimeter(radiation monitor) system. The portable monitor consists of aGeiger-Muller tube (GM tube) with an event counter which records thenumber of ionizing events. There is a readout display and an audioalarm. The problem with the GM tube is that its response is not linearwith the energy of the radiation so its accuracy varies with radiationenergy, although it is useful for warning.

OBJECTS OF THE INVENTION

It is an object of this invention to provide a radiation detector whichaccurately measures both the total radiation exposure (total dose) andthe rate of exposure (dose rate).

It is another object of the present invention to provide small,lightweight, integrated radiation detector assemblies whichelectronically record the degree of radiation exposure.

It is an additional object of the present invention to provide aradiation detector assembly which is separably mounted in a calibrationand display unit capable of calibrating the assembly and displaying theradiation count or the dose rate.

It is an additional object of the present invention to provide aradiation monitor usable whenever ionizing radiation needs to bedetected and measured, for example, area monitors, survey notes,radioactive gas detectors and quality assurance measures.

SUMMARY OF THE INVENTION

In one embodiment, the radiation detector includes a radiation detectionassembly and a detector control and . interface unit. The detectionassembly is a plurality of detection subassemblies. Each subassemblyincludes a hemispheric bubble of electrically conductive tissueequivalent plastic which defines a volume of gas within the bubble. Thegas is adapted to be ionized by radiation incident thereon. Anintegrated circuit (herein IC) is mounted below the volume of gas. Acollecting electrode, on the surface of the IC, is in direct contactwith the gas and collects ions resulting from the ionization of the gasby the radiation. The IC includes an amplifier that incorporates thecollecting electrode. The detector control and interface unit conditionsthe signal from the amplifier and buffers that signal. In oneembodiment, the unit includes a sensing amplifier that acts as acomparator, and a counter which is used to control the detectionsubassembly. The collecting electrode is a control gate for anamplifying transistor in the incorporated amplifier. An electric fieldwithin the volume of gas moves ions of one polarity toward thecollecting electrode. The control gate/collecting electrode is biased toa predetermined level which changes due to the collected ions andtherefore the output of the amplifying transistor is a signalrepresentative of the amount of ions collected. The signal is applied tothe interface and passed to the sense amplifier. When the conditionedsignal passes a predetermined threshold, the counter is triggered and isincremented. Triggering the counter also commands a circuit to clear orrestore a predetermined bias level to the control gate (the collectingelectrode) of the amplifying transistor. The interface may additionallyinclude a dose and dose rate computer, a memory and a communicationssection. In further embodiments, the voltage level (bias) of thecollecting electrode is switched from a high and to a low level or viceversa upon receipt of a triggering pulse, thereby eliminating the needto electrically connect a voltage source to the collecting electrode toclear the accumulated charge.

Multiple electrodes can be used on the surface of the IC and configuredeither as collecting electrodes or biasing electrodes. In the latterconfiguration, the flux lines of the electric field extend between thebiasing electrodes and the collecting electrodes. Otherwise, theelectric field extends between the collecting electrodes and theinterior surface of the conductive plastic defining the bubble of gas.

Another embodiment of the present invention utilizes several volumes ofgas disposed above a single IC. In this setting, the IC has a pluralityof collecting electrodes in direct contact with each volume of gas. Inan additional embodiment, one volume of gas is displaced from atop theIC by a small distance. In this situation, the IC and the correspondingcollecting electrode in the offset volume of gas are mounted on thesubstrate. The electrode is electrically coupled to the amplifier in theIC.

In other embodiments, the radiation detector mates with a calibrationand display unit. Further, a plurality of radiation detectors can beconfigured as an air monitor or as an area monitor.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the concluding portion of thespecification. The invention, however, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 illustrates a functional block diagram of the radiation detector;

FIGS. 2A and 2B illustrate a partial cross-sectional view of two volumesof gas, or ion chambers, atop an integrated circuit;

FIG. 3A illustrates another embodiment wherein one chamber is disposedproximate to but offset from the integrated circuit;

FIG. 3B illustrates an embodiment wherein two ion chambers areconcentric and both are disposed atop the integrated circuit;

FIG. 4 illustrates a cutaway top view of an embodiment of the presentinvention showing ion chambers atop two integrated circuit elements;

FIG. 5 illustrates the integrated circuit having surface electrodes E₁,E₂ and E₃ ;

FIG. 6 illustrates the cross-sectional view of the ion chamber withmultiple electrodes E₁, E₂ and E₃ in direct contact with the gas in thechamber;

FIGS. 7A, 7B and 7C illustrate respectively multiple ion chambers per ICand multiple chambers each having a corresponding IC;

FIGS. 8, 9 and 10 schematically illustrate the electric fieldconfigurations with multiple electrodes in an ion chamber;

FIGS. 11 and 12 illustrate circuits, in block diagram form, whichmeasure the voltage of the sensing or collecting electrode;

FIG. 13 illustrates a flyback circuit which applies an increased voltagebias to a bias electrode;

FIG. 14 illustrates another flyback circuit;

FIG. 15 illustrates a block diagram circuit for measuring the amount ofradiation and counting the radiation dose;

FIG. 16 illustrates a block diagram circuit that changes the rate atwhich the voltage changes on the collecting electrode dependent upon theradiation count;

FIG. 17 illustrates a block diagram circuit for compensating currentleakage between the drain of switching transistor T₁ and the ICsubstrate;

FIG. 18 illustrates further leakage compensation circuit;

FIG. 19 illustrates a block diagram circuit that varies the voltage biasapplied to the bias electrode thereby eliminating the switchingtransistor;

FIGS. 20A and 20B illustrate a block diagram circuit that changes thevoltage level applied to the collecting electrode and the timing diagramtherefor, respectively;

FIG. 21 illustrates a block diagram circuit that changes both voltagelevels applied to the bias electrode and the collecting electrode.

FIG. 22 shows a timing diagram for the circuit in FIG. 21;

FIG. 23 illustrates multiple electrodes coupled to a selecting means inblock diagram form;

FIGS. 24a, 24b and 24c schematically illustrate a power circuit, aflyback circuit and a capacitive voltage multiplier for the presentinvention;

FIG. 25 illustrates a memory and communications section for theradiation detector;

FIG. 26 illustrates the power an-d communications paths for multipleintegrated circuit elements in the detector;

FIG. 27 illustrates an exploded view of the radiation detector and acradle display unit which mates with the detector;

FIG. 28 illustrates a block diagram circuit for the display unit;

FIG. 29 illustrates a detector calibration and display device; and,

FIG. 30 illustrates an area monitor utilizing four detectors.

DETAILED DESCRIPTION

This invention relates generally to a radiation detector andparticularly to a radiation detector with a volume of ionizable gas atopa solid-state integrated circuit.

FIG. 1 illustrates a functional block diagram of the radiation detector.Radiation detector 10 includes two general sections, a radiationdetection assembly 12 and a detector control and interface unit 14.Radiation detection assembly 12 includes radiation detectionsubassemblies 1, 2 . . . n-1, n. Each detection subassembly includessimilar items as those depicted in detection subassembly 1. An ionchamber 16 holds a volume of ionizable gas atop an integrated circuithaving a collecting or sensing electrode in direct contact with the gas.A field generator 18 develops an electrical field within the volume ofgas and moves the ions in the gas created by radiation. The signal fromthe collecting electrode is applied to amplifier 20 and is subsequentlyapplied to a leakage compensation and discharge controller₁ 22 indetector control and interface unit 14. The leakage compensation isdiscussed in detail below with respect to FIGS. 15 through 18.Alternatively, or in addition to, the detection subassembly 1 mayinclude leakage compensation circuit A 24. Since the collectingelectrode attracts ions in the gas due to the bias placed thereon, thesubassembly includes charge removal device 26 that is coupled to theinput of amplifier 20 and the input of field generator 18. The specificcircuitry for charge removal device 26 and its operation is describedlater with respect to FIGS. 15 through 22.

Leakage compensation and discharge circuit₁ 22 controls charge removaldevice 26. In the detector control and interface unit 14, a leakagecompensation and discharge circuit is associated with each radiationdetection subassembly. Leakage compensation and discharge unit₁ 22 iscoupled to dose and dose rate calculator and controller 30, memories 32,human interface 34 and electronic interface 36. The dose and dose ratecalculator and controller generally determines the total amount ofradiation the radiation detector has been subjected to as well as therate at which the detector detects the radiation. These items are storedas radiation count data in the memories 32. The radiation detector maybe embodied as CMOS integrated circuit elements to reduce powerrequirements and hence reduce the size of a power supply. The power canbe internal to the detector and can be a battery; the power supply andthe battery are not shown in FIG. 1. Various detection subassemblies andassociated circuits in the detector control can be embodied as aplurality of integrated circuits (ICs). These ICs can be coupled to amicrocomputer on a chip that functions as dose and dose rate calculatorand controller 30, memories 32, human interface 34 and electronicinterface 36. In another embodiment, a substantial portion of thedetector can be embodied as a single IC. In general, the human interface34 can include a display device which displays the total radiationcount, i.e., the dose, or the dose rate. The human interface could alsoinclude actuable switches such that the dose and dose rate could bedisplayed upon command. Alternatively, those values could becontinuously displayed. Further, the human interface may include alarmcircuitry which would audibly, visually or otherwise (such as tactile orolfactory) provide an alarm to a human indicating that a certain dosethreshold or a dose rate threshold has been exceeded. Electronicinterface 36, in another preferred embodiment, could include acommunications section linking a plurality of radiation detectorstogether. The electronic interface in combination with calculator andcontroller 30 and memories 32 could provide for the setting orprogramming of the dose threshold or dose rate threshold for the alarm.Calculator and controller 30 is the controller for interfaces 34 and 36,memories 32, and the other components in unit 14.

In another alternative embodiment, detection subassemblies 1, 2, n-1 andn could be constructed to sense different degrees of radiation.Detection subassembly 1 could detect significantly lower levels ofradiation than subassembly 2 and calculator and controller 30 can beprogrammed to select the output from subassembly 2 only after the outputof subassembly 1 reaches a predetermined value. In a general sense,detector control and interface unit 14 buffers the signal from radiationdetection assembly 12 and conditions the output signal from thosesubassemblies as well as processes those output signals.

FIG. 2A illustrates a partial cross-sectional view of a hemisphericplastic bubble 94 defining two volumes of gas, large volume 96 and smallvolume 98. Integrated circuit 100 is disposed immediately below gasvolumes 96 and 98 and has surface portions 102a and 102b in directcontact with the substantially discrete volumes of gas. Althoughpresent, the electrodes on surfaces 102a and 102b are not illustrated inFIG. 2. Integrated circuit 100 is mounted on base 104. Connecting wire106 extends between integrated circuit 100 and other components in theradiation detector located at other places on substrate base 104.

It is known to persons of ordinary skill in the art that the domesticand international government regulations require and/or recommendmeasuring dose at different tissue depths. Therefore, several ionchambers are included in the radiation detector. The geometry of eachion chamber can be altered to match the radiation response of the humanbody. Likewise, different wall materials can be used rather than tissueequivalent plastic. Also, different types of gas can be utilized to varythe detection of prescribed types or energies of radiation. Thethickness of the ion chamber wall, if made from tissue equivalentplastic, determines the depth, into the human body, at which theradiation is being measured. An example of tissue equivalent plastic isa polyethylene based plastic with mixture of carbon black, calciumfluoride, and nitrogen containing plastics that approximately match theelemental characteristics (C, N, H and O) and effective atomic number ofhuman muscle.

Gas volumes 96 and 98 are not illustrated as being completely isolatedand further the plastic, which forms bubble 94, extends laterally alongsurface 108 of substrate 104. Precise isolation between volumes 96 and98 is not required because ions generated by the radiation will move ineach volume dependent upon an electric field established therein. Few ifany ions pass between gas volume 96 and gas volume 98. The plastic isnot illustrated as being specifically mounted on surface 108 ofsubstrate 104 because of manufacturing constraints. Also, FIG. 2 is amagnified view of the ion chamber and the gap between plastic 94 andsurface 108 may be exaggerated in that illustration.

FIG. 2B illustrates IC 100 mounted on substrate 104. Additionally, athin tissue equivalent plastic insert layer 101 is interposed betweenbubble plastic 94 and substrate 104 by mounts 103 and 105. Tissueequivalent plastic dots 107 and 109 are chosen as the collectingelectrodes in order to obtain the proper electron equilibrium in the ionchamber. The geometry of the dots can be used to optimize the electricfield. Layer 101 and dots 107 and 109 are an integral part of the ICsurface. Other collecting electrode materials may be used to gaindifferent advantages.

Plastic bubble 94 is molded to define two gas volumes 96 and 98. In onepreferred embodiment, all the electronics for the radiation detectorreside on one substrate. The ICs, one of which is IC 100, are bondeddirectly to the substrate. The circuit can be injection molded into thebottom case of the radiation detector or be a rigid board or a flexiblesubstrate which is attached to the bottom case. It is important that theintegrated circuits align with the ion chambers on the top half of thecase. Also, it is important that water does not leak into the radiationdetector after it is assembled. An adhesive type epoxy may hold the twohalves of the detector together or they can preferably be weldedtogether. The thickness of the thinnest chamber wall is 0.003 inches;therefore, further protective structures may be required for thatchamber holding that volume of gas.

FIG. 3A illustrates another embodiment of the present invention whereinlarge gas volume 96 is immediately proximate and atop integrated circuit100 but small gas volume 98 is disposed proximate to but offset from IC100. Small volume 98 should be as close as possible to the IC tominimize capacitance.

An important feature of the present invention is the presence of thecollecting electrode in direct contact with the gas volume, e.g., inFIG. 3A, electrode 110 in gas volume 96. The collecting electrode is ona surface segment of the IC. The surface segment is a portion of thestructure which defines the volume of gas. However, the claims appendedhereto include the concept that the collecting electrode may be bondpads, sense pads or electrically conductive, plastic structures bondedto, overlayed on or connected to the IC. In a strict sense, thecollecting electrode may encompass all of the surface segment of the ICin contact with the gas. In any case, the IC is in close proximity tothe volume of gas and in a preferred embodiment is immediately below thevolume of gas. A protective covering, a non-conductive layer, or otherstructures placed on the surface of the IC, exclusive of the surfaceportion having the collecting electrode thereon, is encompassed by theuse of the term "integrated circuit element" in the claims.

Returning to FIG. 3, collecting electrode 110 (the size of which isexaggerated in FIG. 3A) is on surface 102 of integrated circuit 100 andcollects the ions produced by the radiation within gas volume 96. Withrespect to smaller gas volume 98, collecting electrode 112 is disposedon substrate 104. In a similar fashion to collecting electrode 110,collecting electrode 112 is in direct contact with the potentiallyionized gas in gas volume 98. Coupling wire 114 electrically couplescollecting electrode 112 to appropriate electronics in integratedcircuit 100.

FIG. 3B shows an embodiment wherein two ion chambers or gas volumes 96and 97 are concentric and both are disposed atop IC 100. The lower gasvolume 96 is a low dose rate ion chamber and chamber or volume 97 is thehigh dose rate chamber. The volumes are physically separated by barrierwall 95. Gas is capable of passing between volumes 96 and 97 via passage99. In one embodiment, barrier wall 95 is an electrically insulatingplastic support having on its radially outer surface a collectingelectrode structure (not shown but may be a layer of conductive plastic)for the high dose chamber or volume 97. In that embodiment, the radiallyinner surface of wall 95 includes a biasing or counter electrode, whichis described in detail later with respect to the electric fieldgenerating means, for the low dose chamber or volume 96. In anotherembodiment, wall 95 is not made of electrically insulating material butis an electrically conductive plastic material such that the low doserate counter electrode and the high dose rate collecting electrode arethe same entity. As will be described later, control circuitry selectsthe effective range of the detector subassemblies by selecting whichchamber is being monitored. In FIG. 3B, the high dose rate chamber(volume 97) has a more uniform electric field.

FIG. 4 illustrates an alternative embodiment of the present inventionshowing integrated circuits 120 and 122 associated with ion chambers 124and 126, respectively. Only a surface segment of each IC is proximatethe respective volume.

FIG. 5 illustrates the top surface 128 of an integrated circuit 130.Bond pads 132 are illustrated along the right-hand portion of integratedcircuit 130. These bond pads provide electrical contacts to theintegrated circuit. On surface 128, electrodes E₁, E₂ and E₃ areillustrated as being concentric.

FIG. 6 is a cross-sectional view of integrated circuit 130 which hasbeen mounted on base 134 and below an ion chamber. Plastic bubble 136defines gas volume 138. Electrodes E₁, E₂ and E₃ are in direct contactwith the gas in gas volume 138.

FIG. 7A shows a further embodiment of the present invention utilizingmultiple ion chambers 140, 142 and 144 disposed atop integrated circuit146. Ion chambers 140, 142 and 144 include electrode sets 148, 150 and152, respectively. FIGS. 7B and 7C show a "snowman" configuration. The"snowman" configuration places the IC or a corner thereof into a fullyspherical ion chamber. See IC 145 partially exposed to chamber 147 inFIG. 78. This gives almost 4π uniform detection. The spherical volumeinside the inner wall defining chamber 147 is filled with gas. Thecorner (or edge of the IC if a single IC is exposed to all the chambers)of the IC would have an appropriate (probably spherical) electrode gluedto it to collect ions. Thus, the angular response is uniform except whenthe radiation passes through the case in the black or from one ionchamber to the other. FIG. 7C shows plastic case 141, capable of holdingbatteries and other components and IC 145 extending beyond the outerwall of the bubble defining chamber 147.

In order to efficiently collect ions within the gas volume, an electricfield is generated therein such that the ions move in accordance withthe electric field. In FIGS. 8, 9 and 10, flux lines are illustrated asintersecting with and/or extending from the electrodes. In general, bycontrolling the electric field, different regions of the gas volume canbe swept or sensed by the electronics in the radiation detector. In thefigures, the semicircular line 154 represents the interior surface ofthe plastic bubble of the ion chamber. V_(s) is the sensing voltage andusually designates the collecting electrode; 0 v represents a groundedelement; and V_(s1), V_(s2) and V_(s3) represent different collectingelectrodes set at different predetermined voltages.

In FIG. 8, electrode E₁ is the collecting electrode and is set atvoltage +V_(s). It is to be understood that the voltages illustrated anddiscussed herein are only exemplary and any discrete voltage levels canbe used in place of the described and illustrated voltages. For example,rather than having a positive voltage at the collecting electrode, anegative voltage can be applied thereto. In that case, positive ions arecollected at the collecting electrode rather than negative ions asdiscussed with respect to a +V_(s) at the collecting electrode. Also,the 0 v could be any internal ground voltage other than zero volts whichis designated as ground for the radiation detector.

In FIG. 8, electrode E₁ is the collecting electrode and is electricallybiased to predetermined level +V_(s). V_(s) implies that this electrodeis connected to a sensing circuit. The voltages E_(n) imply connectionto a voltage source with no measurement of collected charge being done.Electrodes E₂, and E₃ operate as biasing electrodes and are at 0 v. Theone end of the flux lines of the electric field in FIG. 8 intersectscollecting electrode E₁ and the other end intersects biasing electrodesE₂, and E₃. Also, since interior surface 154 will be typically groundedand since the plastic is conductive in nature, the electric field doesextend to that interior surface. In this situation, when ions aregenerated in the volume of gas, negative ions will move towardscollecting electrode E₁ due to the positive voltage level thereon andvoltage V_(s) will change, although the change may be minute, due to theaccumulation of charge on electrode E₁. In order to obtain the electricfield, the radiation detection subassembly includes means for generatingthe electric field. The strength of the electric field generally dependsupon the voltage differential between the collecting electrode andanother element within or without the volume of gas. Therefore, thestrength of the electric field can be varied by changing the voltagedifferential, at least in FIG. 8, between electrode E₁ and electrodes E₂and E₃. By applying a lower voltage to electrodes E₂ and E₃, theelectric field within the volume of gas would increase. Similarly, byraising the voltage V_(s) on collecting electrode E₁, the electric fieldincreases.

In FIG. 9, interior surface 154 is grounded at 0 v, electrodes E₁ and E₂are biased to voltage +V_(e) and electrode E₃ is selected as thecollecting electrode and is biased to +V_(s). Since electrode E₃ isselected as the collecting electrode, the region swept is that regionbetween electrode E₃ and surface 154 and is limited to the radiallyouter sectors of the volume. A complex conically cylindrically symmetricregion is therefore swept.

In FIG. 10, any one of electrodes E₁, E₂ and E₃ can be the collectingelectrode since V_(s1) need not equal V_(s2) or V_(s3).

The means for generating the electric field need not be a battery. Itcan be two dissimilar materials which are physically and electricallyconnected at one end. For example, if the ends of a piece of copper anda piece of steel are joined, a voltage develops across the free ends ofthe copper and steel due to the work function difference between thedifferent materials. This voltage differential may be sufficient tocreate the electric field for the IC dosimeter. Particularly, a goldplate or element and a carbon based plastic may be utilized to generatean electric field in this fashion due to the work function between goldand the carbon based plastic. Also, the biasing electrodes do not haveto be exposed to the gas (excepting the collecting or sensingelectrodes) since a field can be developed by conductors either withinthe IC or within the hemispheric bubble defining the volume of gas.

In operation, the radiation interacts with the gas in the ion chambergenerating ions which move in the electric field. The ions of onepolarity are collected on the exposed collecting electrode and thecharge signal therefrom is amplified. If the collecting electrode isbiased to a positive voltage with respect to the other electrodes,negative ions will be attracted and the voltage +V_(s) will decreasebased upon the amount of collected ions. The number of ions generated isproportional to the dose received. Ideally, all the ions generated arecollected. The gas in the chambers should be under a slight pressure toprovide some crush resistance when thin covers are used for thedetection of beta particles. The choice of gas is determined by theenergy response desired. Air, nitrogen, argon or tissue equivalent gasare possibilities. The use of air would result in the radiation beingmeasured in Roentgens (R). Tissue equivalent gas measures radiation inrad (radiation absorbed dose) or Gy (gray unit which equals 100 rads).

The ion chamber performance is not ideal. The greater the radiation doserate, the greater the number of ions generated. However, for finiteelectric fields, the ions are not collected instantly, so theconcentration of ions in the gas increases with increasing dose rate.This results in some of the positive ions recombining with negativeions. These ions cancel and are not collected by the electrodes. Thus,the charge collected is decreased by this recombination and themeasurement is no longer proportional to the dose received.

The minimum size of the ion chamber is determined by the minimum doserate to be reliably detected. The dose rate permissible in anunrestricted area, an area which is classified as unrestricted bygovernment regulations, is 2 mR/hr. A reasonable charge sensitivity foran integrated circuit amplifier is 1000 electrons since engineeringliterature describes an amplifier that can sense 1 mv with an inputcapacity of 1×10⁻¹⁴ F. Using the definition of 1 mR as being the amountof radiation required to generate 2000 ion pairs/mm³, a volume of 180mm³ would average one pulse every five seconds at a dose of 2 mR/hr.

The shape of the ion chamber is controlled by the conflicting desires tohave as high an electric field as possible and as low a capacitance aspossible. The higher the electric field, the faster the ions move andhigher the dose rate which can be accurately monitored. The lower thecapacitance, the smaller the minimum charge and hence the smaller thedose which can be measured. A large area parallel plate arrangementcould give the highest field. Concentric spherical surfaces would give alow capacitance. As mentioned above, at high dose rates, recombinationoccurs.

Different ion chambers and measurement circuits can accurately measuredifferent dose rates. In certain situations, monitoring needs to occurover a wide range of dose rates, such as a survey instrument, or an areamonitor which must take measurements during an accident as well asnormal times. Or, some information about the radiation dose as afunction of energy may be needed so several ion chambers are needed. Thehigh dose rate chamber would be significantly smaller and have a higherfield than the low dose rate chamber. For the high dose rate chamber,the collecting electrode need not be directly attached to the integratedcircuit as illustrated in FIG. 3. The added capacitance of connectingwire 114 can be tolerated because ion chamber 98 does not need to besensitive to miniscule doses. The control electronics in the detectorcontrol and interface unit 14 monitor the dose rate from each detectionsubassembly and use the chamber which is most accurate.

Alternatively, two or more electrodes in one ion chamber can be used. Bychanging the voltages applied to these electrodes, the volume swept bythe collecting field can be changed. Examples of these are illustratedin FIGS. 8, 9 and 10. There are an unlimited number of electrodeconfigurations with various advantages. FIG. 8 shows the bias appliedwhen measuring a low dose rate. All charge is collected at centerelectrode E₁. Charge is collected from the total volume. FIG. 9 showsthe bias conditions for which charge is measured in a smaller, highfield, volume. In FIG. 10, the collecting electrode and hence the volumeswept can be selected.

FIGS. 11 and 12 illustrate circuits which measure the current to thecollecting electrode 155 rather than the charge due to the collection ofions on that electrode. In FIG. 11, one input of amplifier 157 is biasedto a voltage level dependent upon the power source V¹ and the value ofresistor 159. The voltage changes due to the voltage drop acrossresistor 159 as the collected current is conducted through it. As isdiscussed in detail later, electrode 156 is a bias electrode thatestablishes the electric field in the volume of gas. In FIG. 12,resistor 161 provides a feedback voltage signal that is a basis forcomparing the signal obtained from collecting electrode 155.

Since the electric field is controlled in part by the voltage applied toa particular electrode, FIGS. 13 and 14 illustrate flyback circuits toincrease the voltage levels and hence increase the electric field. Theuse of flyback circuits permits bias control circuitry for a particularion chamber to increase the bias field V_(e)(g) (depicted as V_(e) inFIG. 9) as the dose rate increases. For example, for every factor of 10increase in the dose rate, the bias is increased by the square root of10 to maintain recombination losses at the same level. The flybacktransformers 160, 160a and 160b are triggered via transistor T_(g) afterthe dose rate exceeds some rate threshold. The charge on capacitor C_(f)is increased due to the release of energy from inductors 160 and 160awhen T_(g) is turned off. If the flyback transformer is not being used,the battery voltage is applied to V_(e) with substantially no voltageloss other than the diode. The detector control in FIG. 1 can beconfigured to control the flyback circuits in this manner. This powercircuitry is part of the detector control as is any required voltageregulation circuitry.

FIGS. 15, 16, 17, 18, 19, 20 and 21 illustrate electrical block diagramsfor the radiation detector. In FIG. 15, collecting electrode 170 iselectrically biased to predetermined voltage level V_(s). Bias electrode171 establishes the electric field in the gas and is coupled to powersupply 173. The dashed box 175 on the right indicates that thosecomponents are part of one radiation subassembly in FIG. 1. The dashedbox 177 indicates components considered part of detector control andinterface unit 14 in FIG. 1.

The collecting electrode is exposed to the volume of gas. The collectingelectrode is also the control gate for amplifying transistor T₀, i.e.,the collecting electrode is "incorporated" into the amplifier embodiedby transistor T₀. The source of amplifying transistor T₀ is coupled tovoltage V₂ and the drain of the amplifying transistor places a signal online 172 representative of the amount of accumulated charges on theelectrode and hence the radiation sensed by the detector subassembly.Buffer amplifier 174 isolates amplifying transistor T₀ from the rest ofthe circuitry and amplifies T₀ 's output. V₀ is applied to senseamplifier 176. Sense amplifier 176 determines when the V₀ drops below apredetermined threshold V_(ref) and generates trigger signal for counter178. The trigger signal is also applied as a clearing control signal toa circuit which restores voltage V_(s) to the collecting electrode orclears the accumulated charge from the electrode. If V_(s) is a positivevoltage with respect to the voltage on 171, negative ions will beattracted to collecting electrode 170 and voltage V₀ will fall dependentupon the accumulated charge. When V₀ falls below V_(ref), senseamplifier 176 triggers counter 178.

Switching transistor T₁ applies a clearing voltage V_(c1) to the controlgate of amplifying transistor T₀. Clearing voltage V_(c1) is developedacross capacitor C1. Switching transistor T₁ is turned on by the clearcontrol signal, i.e., the trigger signal, from sense amp 176 andthereafter couples capacitor C1 to the control gate of amplifyingtransistor T₀. During the trigger pulse, inverter 180 turns secondswitching transistor T₂ off and therefore isolates V_(chg) fromcapacitor C1. When the trigger signal is removed, second switchingtransistor T₂ is turned on and capacitor C1 is charged by voltageV_(chg). It is recommended that transistors T₁ and T₂ do not conduct atthe same time. In this sense, the turn off time of the transistors mustbe quick and the turn on time must be slow.

In one embodiment, transistors T₀, T₁ and T₂ as well as buffer amplifier174, sense amplifier 176, counter 178 and capacitor C1 are all disposedwithin the integrated circuit. The buffer and sense amplifiers may becombined. Other data processing components in the detector control andinterface unit are downstream of counter 178 and may or may not be onthe same IC. Collecting electrode 170 is directly exposed to the volumeof gas and may be embodied as a sense pad which is placed above aconductive channel running internally into the integrated circuitelement. The sense pad may be larger than the internal conductivechannel because the sense pad can be spread over a top layer ofinsulation on the surface of the integrated circuit. The preciseconstruction of an integrated circuit having these electrical componentsis known to persons of ordinary skill in the art. CMOS technology can beutilized to obtain the low power detector described herein.

Although these components are constructed as a single IC, their functioncorresponds to the functional block diagram in FIG. 1 as follows: senseamp 176 is part of amplifier 20; counter 178 corresponds to part ofcalculator and controller 30, transistors T₁ and T₂ and associatedcircuitry correspond to charge removal device 26. Counter 178 can bereset or re-zeroed on a periodic clock signal from computer 30.Alternatively, the device control and interface unit could operate onpurely analog signals from the subassemblies rather than digitalsignals. As is described in detail below, the charge removal, theelectric field generation and leakage compensation are all interrelated.

The use of switching transistor T₁ to provide a clearing voltage(V_(c1)) to the control gate of amplifying transistor T₀ presents aproblem regarding the current leakage, ILEAK, from the transistordiffusion to the IC substrate. The current leakage is designated bydashed lines as ILEAK in FIG. 15 from the integrated circuit substrateto the drain of switching transistor T₁. This current leakage ILEAK willbe sensed as an accumulated charge and hence a dose. A rough calculationindicates that this leakage could cause a pulse every eight seconds. Fora 0.18 cm³ chamber, this gives a background reading of radiation of 1.25mR/hr which is unacceptable. The effect of leakage should be less than 1mR/day. Corrective measures for minimizing the effect of ILEAK arediscussed later.

A person of ordinary skill in the art recognizes that the voltage levelsdiscussed with respect to FIG. 15 could be reversed. In that situation,positive ions would be attracted to the collecting electrode andamplifying transistor T₀ would either turn on at a certain voltage levelV_(s) or simply amplify the voltage V_(s) based upon the accumulatedcharge. In that situation, voltage V₀ would steadily increase and senseamp 176 would provide a trigger when voltage V₀ exceeds referencevoltage V_(ref). Capacitor C1 would then discharge the accumulatedcharge from the gate of transistor T₀ and capacitor C1 would thendischarge via transistor T₂ to the voltage source. Also, the buffer ampand sense amp could be inverting or non-inverting with compensation madeelsewhere in the circuit.

FIG. 16 illustrates collecting electrode 170 and biasing electrode 182as well as a rate change circuit that includes transistor T_(R). Itemsto the left of the double dashed line 85 are considered part of thedetection subassembly; items to the right are part of the detectorcontrol. The biasing voltage V_(e) is applied to biasing electrode 162providing an electric field that extends between collecting electrode170 and biasing electrode 182. The bias voltage can be controllably setby a control circuit 184 coupled to the output of counter 178. Asdescribed earlier with respect to FIG. 12b, biasing voltage V_(e) can becontrollably set at a plurality of discrete levels dependent upon thecount in counter 178. Particularly, the flyback circuits of FIGS. 13 and14 could be used to apply this increased biasing voltage.

Another aspect illustrated in FIG. 16 is the circuit for changing therate upon which the control gate of transistor T₀ changes. TransistorT_(r) is controlled by rate change control signal TR gate from controlcircuit 184. When rate change control signal TR gate is high, capacitorC_(r) is electrically coupled to the control gate of transistor T₀.Therefore, accumulated charge on collecting electrode 170 must charge ordischarge capacitor C_(r) and hence the rate at which signal V₀ changesis decreased because of the added capacitance.

The electronics has a maximum count rate set by its speed. If thismaximum count rate becomes a limitation rather than the chargerecombination rate discussed earlier, it is necessary to add the extracapacitance C_(r) to reduce the sensitivity of the detectionsubassembly. When transistor T_(r) is conductive, the amount of chargerequired to trigger sense amp 176 is increased. For a constant dose, ifthe counter is incremented by a number greater than 1 for each triggerpulse from sense amp 176, the calibration in the counter per collectedcharge stays constant but the period between counter updates isincreased. Therefore, the speed of the electronics is no longer alimiting factor. In this sense, the control circuit 184 would monitorthe dose rate and provide rate change control signal TR gate when thedose rate exceeds a predetermined level.

As stated earlier, the major difficulty with clearing or restoringvoltage V_(s) to the control gate of transistor T₀ via transistor T₁ isthe current leakage ILEAK from the integrated circuit substrate to thedrain of transistor T₁ and hence the collecting electrode. The roughestimate earlier presented indicates that this leakage may cause a pulseevery eight seconds.

One method of compensating for ILEAK is simply to have the radiationdetector not register any pulses unless the pulses are less than eightseconds apart. This operation is simply pulse stream manipulation. Asecond simple method is to have the radiation detector not register anydose when it is disabled or turned-off. The detector could be stored ina charging/disabling cradle during that time.

FIG. 17 illustrates a block diagram circuit for analog currentsubtraction used to compensate for the leakage current. Currentgenerator ICOMP is controlled by ICOMP control 186. The ICOMP controlwould be sent during calibration of the detector. As is known by personsof ordinary skill in the art, if the voltages were reversed in FIG. 17,ILEAK would be a current source and ICOMP would be a current sink. Ineither situation, ICOMP is controllable by ICOMP control 186. Thedifficulty with this system is having ICOMP follow ILEAK as conditionsvary.

FIG. 18 illustrates another alternative embodiment of a circuit tocompensate for ILEAK. In that figure, the sensing circuit is indicatedby character "a" such that transistor T₀ is now T_(0a). T_(0a) iscoupled to buffer amplifier 174a, sense amp 176a and counter 178a. Aduplicate circuit is illustrated with character "b." Therefore, thecounterpart to transistor T_(0a) is T_(0b), buffer amp 174a isduplicated as amp 174b, etc. The primary distinction between theduplicate circuit and the sensing circuit is that the control gate fortransistor T_(0b) is not coupled to the collecting electrode in theduplicate circuit.

As long as T_(1a) and T_(1b) are equal in size and do not contain anygross defects, the leakages ILEAKA and ILEAKB should be almostidentical. In other words, both leakage currents should track each otheras conditions vary. Therefore, the true dose exposure can be determinedby taking the difference between the number of pulses received bycircuits a and b.

One compensation method utilizes a rate compensator 188. It senses whenthe pulse rate in sense amp 176a is less than the pulse rate in senseamp 176b and prevents an incrementing counter 178a. Thus, no dose isregistered unless it is in excess of ILEAKB. A second method is betteradapted to proportional but unequal ILEAKA and ILEAKB. A prescaler 190decrements counter 178a when the count value from duplicative counter178b equals the compensation count value in leakage compensation memory192. The scaling circuit compensates for the measurement circuits notbeing identical. The leakage compensation memory is loaded duringcalibration and contains the proportionality constant related to the twocircuits leakages.

Another method to reduce current leakage ILEAK is the well isolationinherent in CMOS process. By keeping the well of transistor T₁ equal tothe voltage of the collecting electrode, significantly less leakage willoccur.

FIG. 19 illustrates a further circuit, in block diagram form, foreliminating switching transistor T₁ and thus the source of leakage. Thecollecting electrode is only connected to the control gate of transistorT₀. The bias V_(e)(t) drives a charge of one polarity to the collectingelectrode 170. The single polarity charge accumulates ions at collectingelectrode 170 until sense amplifier 176 triggers counter 178. Controlcircuit 184 changes the bias signal applied to bias electrode 182thereby switching the electric field in the volume of gas to bring ionsof the opposite polarity to collecting electrode 170. The oppositelycharged ions cancel the previously accumulated charge on collectingelectrode 170. In this situation, the minimum voltage V_(e) (t)_(min) isless than V_(s) which in turn is less than the maximum voltage V_(e)(t)_(max). The reference voltage V_(ref) (t) is varied such that thesense amp triggers the counter when signal V₀ exceeds a maximumthreshold level in one instance and falls below a minimum thresholdlevel in a second instance. Therefore, either the reference voltage mustbe switched within sense amp 176 or electrical circuitry be designed todetermine when V₀ passes beyond a predetermined window.

FIG. 20A illustrates a block diagram circuit which changes the voltageof collecting electrode 170 via a coupling capacitor C₀. In thisembodiment, when sense amp 176 triggers counter 178 when V_(coup1) (t)is at one level (see FIG. 20B), control circuit 194 switches couplingvoltage V_(coup1) (t) to a different predetermined level. Therefore, thevoltage V_(s) is biased to a high and then a low predetermined levelbased upon a level control signal applied to level control circuit 194.In this situation, the biasing voltage V_(e) applied to biasingelectrode 182 is at an intermediate level as compared to the maximumcoupling voltage V_(coup1) (t)_(max) and the minimum coupling voltageV_(coup1) (t)_(min). Switching via the coupling capacitors isadvantageous because all ion chambers can have the same counterelectrode potential (V_(e)) and the coupling capacitor is part of theintegrated circuit.

There is an additional complication that the sense amp must now sensetwo voltages so some type of Schmitt trigger, window comparator or dualsense amplifiers must be utilized as sense amp 176. As described earlierwith respect to the dual bias levels, the reference voltage V_(ref) (t)varies between two threshold levels dependent upon the coupling voltage.

FIG. 21 shows a block diagram of another circuit for clearing theaccumulated charge on the collecting electrode. FIG. 22 shows the timingdiagram for the operation of the circuit in FIG. 21. Generally, thepolarity of the electric field is reversed periodically (see V_(z) inFIG. 22) similar to the operation described in FIG. 19, i.e., when V_(D)reaches V_(revL) or V_(revH) or effectively after a certain number ofcounts. Sense amplifiers 176a and 176b trigger a counter or otherdetector control component when the signal exceeds or falls below one oftwo reference voltages V_(ref1) or V_(ref2). However, with the additionof capacitor C_(D), the frequency at which field reversal is required isgreatly reduced, if each time the threshold is exceeded, the voltageV_(D) is changed in a stepwise manner. The relatively small voltage steprestores the voltage of the amplifier input to its original value (seeV_(c) between times t₁ and t₂) and prepares the amplifier to senseanother pulse. This circuit substantially eliminates any inaccuracywhich arises when the field polarity is changed after each pulse. Also,it confers some noise resistance similar to that given by constantcharge removal versus constant voltage reset.

A change in V_(D) indicates one pulse sensed by one of the sense amps.From times t₁ to t₂, these pulses represent charge sensed and thus dosereceived. From times t₂ to t₃, the pulses are simply a result of thechanging V_(z) being capacitively coupled to V_(c).

Even without the conducting path through switching transistor T₁,leakage can still occur through other paths. It may be necessary toinclude a guard ring as one of the electrodes (for example, E₃) aroundthe sensing pad (for example, E₁ or E₂) to minimize leakage over thesilicon dioxide layer in the integrated circuit and the passivationmaterials on that integrated circuit. One method of compensating forstray capacitance and stray electric fields developed by componentsinternal of the integrated circuit is to have the guard electrode at thesame potential as the sensing electrode. The geometry of the guard andthe sensing electrode would be chosen such that the guard receives fewof the flux lines of the electric field but surrounds the sensingelectrode, thereby interrupting any surface leakage from the internalcomponents.

Any of these methods of leakage compensation can be combined with anyion chamber described above. In a currently preferred embodiment, alarge ion chamber would utilize integrated circuit control withoutswitching transistor T₁ and utilize electric field reversal. Then, thesame or a different integrated circuit senses the accumulated chargefrom a second smaller ion chamber utilizing the simplest sensing circuitillustrated in FIG. 15. No leakage compensation is necessary in thissimple circuit because the count from the small ion chamber isrecognized only if the dose rate is high. Also, in the contaminationmonitor discussed previously, this ion chamber configuration would berepeated for each of the three tissue depths at which a measurement isto be made.

FIG. 23 is a further development from FIG. 10. In this situation,selector control 196 actuates selecting means 200 which selects one ofthe electrodes E₁, E₂ or E₃ as the collecting electrode. The accumulatedcharge from the selected collecting electrode would be applied viaT_(s1), T_(s2) or T_(s3) to buffer amplifier 174. In a similar manner,biasing electrodes could be selected to apply different levels ofbiasing voltage for the electric field at different times. Becausedifferent volumes of the gas are swept by the electric field of thedifferent electrodes, changing the biases and the collecting electrodechanges the sensitivity and dose rate limits of the radiation detector.

FIGS. 24a, 24b and 24c illustrate power circuits for the detector. InFIG. 24a, the power from battery 202 is applied directly to ion chamberpower 204 as well as to circuit power 206.

In FIG. 24b, the flyback circuit, earlier illustrated in FIG. 14, iscombined with circuit power 206 and both are coupled to one side ofbattery 158.

FIG. 24c illustrates a capacitive voltage multiplier which increasesbattery voltage without the need for an inductor. Square wave generator210 activates the set of capacitors to achieve this multiplication ofvoltage.

In all the power supply types mentioned above, if the concept ofalternating bias voltage polarity is used, then significant power may belost each time the voltage is switched, unless an inductor or some othermeans is used to store the energy and reverse the voltage of the ionchamber. However, this may not be a serious problem because this circuitis used primarily in low dose applications.

FIG. 25 illustrates, in block diagram form, the memory andcommunications section in the detector control. In one embodiment, thissection is associated with one IC. This communications section is ameans for recovering the radiation count from the counters. The dashedline 212 indicates an interface with a bus structure for transferringdata and command or control signals between the memory andcommunications sections for other ICs. In one embodiment, all theintegrated circuits are connected as is best illustrated in FIG. 26, thepower and communication path diagram. For example, the alarm out line isactivated if any one of the ICs, IC₁, IC₂ or IC₃, generates an alarm.The alarm is passed from IC to IC by the alarm-in/alarm-outinterconnection between the three integrated circuits. The alarm ispassed to the human interface 34 in FIG. 1 when the radiation detectoris, for example, configured as an area alarm monitor or as acontamination monitor. The data out line is coupled to the electronicinterface 36 when the radiation detector is configured as a survey meteror an exposure rate meter. In the latter configurations, the chip enablecommand would be periodically actuated to provide a seemingly continuousradiation readout.

In FIG. 25, the alarm-out line is raised when any line coupled to ORgate 214 is raised: the alarm-in line, the dose alarm/rate alarm linefrom the control circuit/radiation count counters or the cyclicredundant character (CRC) control check circuit 216.

Memories M₁, M₂, M₃, M₄, M₅, M₆, M_(n-3), M_(n-2), M_(n-1) and M_(n) arecoupled to various counters and other devices in the integrated circuit.For example, counter 178 (FIG. 15 and others) may be directly coupled toone of these memory units or may be the memory unit M_(n). Counter 178and control circuit 184 must include some type of memory to trigger thecontrol signal g (see FIG. 14), the change rate signal TR gate (see FIG.16), the ICOMP control (see FIG. 17) and the level and pulse duration ofV_(e)(t) (see FIG. 19) and the coupling voltage (see FIG. 20). Also, theleakage compensation memory is a memory unit.

Shift registers S₁, S₂, S₃, S₄, S₅, S₆ , S_(n-3), S_(n-2), S_(n-1) andS_(n) are connected to corresponding memory units. These seriallyconnected shift registers are supplied with data on the data in line.The CRC space control device 218 is needed to hold the 16 CRC charactersused to confirm accurate data reception without displacing any data fromits proper locations. All of the serially connected registers are loadedduring a data write routine and a shift register write (SRW) controlsignal from counter 220 loads the shift register data into theappropriate memory. Shift control to each shift register is alsoaccomplished by a control line from counter 220.

Counter 220 is activated by a chip enable signal and a clock signalwhich is fed to AND gate 222. The output of the counter is also fed toCRC calculator 224 to indicate when to calculate and output, or check,the CRC. The control input/output circuit 226 is coupled to the chipenable line and to the output of the CRC checker circuit 216. I/0control 226 activates transistor T_(out) and allows the data to bereflected on the data-out line. Also, when the counter 220 determinesthat the last 16-bit word is appropriately checked, it places a value ofthe CRC calculator 224 on the data-out line. The last 16 bits representthe CRC code which is used by the receiving device to determine if thetransmission was accurately received.

Data can be shifted into memory with a shift register read/write controlline. When the read or write operation is completed for the presentchip, the next chip is enabled. To write data from outside, data isshifted from M_(x) to S_(x) by the shift register read/write controlline. Then the shift registers are shifted once on each clock cycle withone bit coming out and also going to the CRC calculator 224. When allthe data is out, the 16-bit CRC is shifted out.

FIG. 26 illustrates the power and communication path for the detectorwith integrated circuits IC₁, IC₂ and IC₃. Power and ground are appliedfrom an internal battery in the detector control unit. The alarm is adaisy chained signal. If the alarm is active, it gets passed along. Theactive alarm signal out of the last chip turns the piezoelectric buzzeron if the detector is configured with an active human interface. Inanother embodiment, the alarm could trigger a communications transmitcommand through the electronics interface. Upon receipt of this transmitcommand, the detector would transmit radiation data, e.g., dose or doserate, to an external device. Data read and write is synchronized by theclock. The clock and all power for the external communication driversand internal shift register is provided by communications power which isin turn supplied by a calibration and display unit.

To read, the chip enable and read line are held low. The read/write isbrought high for X clock cycles and then low. After Y cycles, the chipenable is brought high. Z cycles later, all data in the IC₁ is shiftedserially out the data-out line. When IC₁ is done, it enables IC₂. Zcycles later, the data from IC₂ comes out on the data-out line. Whenwriting, the dosimeter counters are disabled. To write data, theread/write control line is held high and kept high. After A cycles, thechip enable is brought high. After B cycles, the data is serially readin on the data-in line until all shift registers are full. When IC₁ isloaded, it raises the chip enable of IC₂. When all the data is loaded,bringing the write line low before lowering the chip enable line causesdata to be stored into the integrated circuit chip memories.

FIG. 27 illustrates detector unit 310 having ion chambers 312, 314a,314b, 314c, 314d, 314e and 314f. The large ion chamber 312 is mostsensitive to radiation. The smaller chambers 314a through f are lesssensitive but are capable of accurately detecting higher doses and doserates as compared with the larger chamber. Or the ion chambers insidedomes 312, 314 and 317 may all be identical and so have identical doserate responses, but have different wall thicknesses and, thus, bemeasuring dose at different depths into the body. Electrical contacts320 extend from one end of unit 310.

External connections 320 on detector unit 310 are provided to facilitatethe transfer of information, i.e., radiation data, control commands,ground and power signals as necessary. The use of output drivers in thedetector unit that obtain power from an external battery in a cradledisplay unit 322 prevents the possibility that one or more contacts 320would short together and result in a spark or drain of the internalbattery in the detector unit. The only common connection between theinternal circuitry in the detector unit and the external unit such asdisplay unit 322 is ground. Alternatively, data communications can usean optical link, encoded sound, near or far field electromagnetic waves,rather than electrical contacts.

A cradle, interface and display unit 322 is separably mated withdetector unit 310. As illustrated, display unit 322 includes lipportions 324 which mate with ledge or flange 326 on detector unit 310.Display unit 322 includes LCD display 328 and recessed control buttons330. Electrical contacts 320 on detector unit 310 mate withcomplementary electrical contacts not shown in display unit 322. Theillustrated connection 323 to central control is optional since themated detector and display units can operate as a stand alone apparatusor can operate in conjunction with multiple mated units. The radiationdetector unit is separably mated to display unit 322 in order to allowthe detector unit to be regularly tested and appropriately calibrated.The display unit and detector unit can be permanently mated in order toprovide a survey meter, a contamination monitor or other types ofradiation monitors requiring substantially continuous or controllablydisplayble radiation data displays. Further, the geometric configurationof ion chambers 312 and 314a-f is only exemplary. The ion chambers canbe geometrically configured in as many shapes as are permitted bymanufacturing constraints. A grid, barrel or hemispheric geometricconfiguration may be appropriate, respectively, for a contaminationmonitor, directional survey meter and a wide area survey meter.

Display 328 is a means for recovering the radiation count from thecounters. Display unit 322 can also be configured as a programmingdevice to set threshold limits, e.g., dose and dose rate thresholds, inthe detector unit. Control buttons 330 can be utilized to confirm thethresholds input via the buttons and then confirm a successfulprogramming of the detector unit. Since unit 322 can be viewed as aprogramming device, that unit is referred to herein as a programming anddisplay unit.

FIG. 28 illustrates, in block diagram form, the electrical components ofprogramming and display unit 322. Battery 334 is coupled to an optionalvoltage regulator 336 which supplies voltage V_(supply) to microcomputeron a chip 338 (herein microcomputer chip 338) and to connector pin unit340. Connector pin unit 340 matingly couples with pin unit 320 of thedetector unit 310.

Microcomputer chip 338 is coupled to input buttons 342 and display unit344. Microcomputer chip 338, when activated by input buttons 342,generates a data transfer command to detector unit 310. This transfercommand is the read command discussed above with respect to FIGS. 25 and26. The output from the detector unit is placed in a memory which ispart of microcomputer chip 338. Also, the radiation data from thedetector control interface, e.g., the counters, is displayed on display344. Microcomputer chip 338 also programs threshold values into detectorunit 310. For example, microcomputer chip 338 programmably sets thetotal dose alarm threshold, the dose rate threshold and the triggerthreshold for the counter. The total dose alarm threshold is thatradiation count value which, when exceeded, triggers the audible andelectrical alarm in the radiation detector.

FIG. 29 illustrates a calibration and display device 350. The radiationdetector is placed in either of two mounting positions, the calibrationposition 352 or the readout position 354. Calibration unit 350 includesdisplay device 356 and keyboard 358. Printer 360 provides a printed copyof the information obtained from the IC dosimeter. Particularly, duringcalibration, a predetermined amount of radiation, from radiation source357 (shielded by shield 359), is directed toward the detector unit.Calibration unit 350 monitors the resulting radiation data (both totaldose and dose rate as necessary) and then compares that radiation dataagainst accurately predetermined radiation data. This computation iscarried out in microcomputer 362. The detector would then be programmedsuch that the threshold level of the sensing amplifier (a thresholddetermining means) would be set and further the alarm threshold levelsfor the alarm circuitry would be set by calibration unit 350.

When the radiation detector unit is in readout position 354, calibrationunit 350 would generate a transfer data command to the detector and readout all data including the current radiation data from the memory units.Appropriate information is displayed on display 356 and printed out byprinter 360. Additionally, calibration unit 350 could program a date ofcalibration into the radiation detector unit as a historical indicatorin the detector's memory. The calibration unit also resets or clearsselected counters, if necessary, in the detector. Additionally, thecalibrator includes a memory, clock, analog and digital interfacecircuits, and an I/0 computer communications port to transfer datainformation to other computer devices.

FIG. 30 illustrates an area monitor which utilizes a plurality ofradiation detectors DET₁, DET₂, DET₃ and DET₄ mounted on a supportwherein DET₁ is illustrated as directionally oriented or facing oneregion and the others are facing the opposite region. The radiationdetectors are plugged into complementary electrical connectors 364 ofarea monitor 366. In another embodiment, area monitor 366 utilizes atleast four radiation detectors disposed 360° around an area monitor. Amultiple IC detector control 368 periodically obtains the radiationcount values from IC detectors DET₁, DET₂, DET₃ and DET₄ by issuingappropriate transfer commands; accumulates the data and relates the datato the particular detector actuated thereby indicating direction, andrelates the data to date and time information; and during otheroccasions periodically communicates via communications circuit 372 to anexternal command unit. Area monitor 366 would include its own powersource 374 to enable the area monitor to be self-sufficient and to powerthe detectors.

Area monitor 366 is generally an environmental monitor which providesinformation regarding the direction as well as the amount of theradiation. A further embodiment of the area monitor is the addition ofair blower or air pump 410 coupled to air monitor interface 412. Byforcing air over radiation detector DET₁ 320, the monitor measures theamount of radiation in the air. Further, an activated absorbingsubstance 411 can be interposed in the path of the forced air to trapparticles or gases therein. Radiation detector 1 is mounted proximateabsorbant 411 to measure the radiation output therefrom.

The radiation detector may include some components to eliminate thepossibility of data loss. An EEPROM on the integrated circuit could beutilized such that battery failure does not result in a loss of data.Further, the radiation detector could chirp a "low battery" signal whenthe internal battery reached a predetermined low value. A person ofordinary skill in the art recognizes that the human interface alarm,sounded by the detector, could include a visual alarm as well as anaudible alarm. Further, the alarm signifying an overexposure ofradiation (total dose) could be different than the alarm signifying anunacceptably high dose rate, i.e., different intensity, frequency and/orduty cycle.

While only certain preferred features of the invention have been shownby way of illustration, many modifications and changes can be made. Itis to be understood that the appended claims are intended to cover allsuch modifications and changes as fall within the true spirit and scopeof the invention. For example, transistor T₀ may be part of adifferential amplifier or the collecting electrode may be a voltagefollower input. Transistors T₁ and T₂ may be two of many additionaltransistors. Also, the audible alarm could require a square wavegenerator as illustrated in FIG. 24.

This concept can be applied to radiation detectors which presently useGeiger-Mueller tubes, scintillators and photomultipliers, or solid statedetectors where the decreased absorption of a gas filled ion chamber,when compared to a solid material, is not important. Also, due to theirlow input capacitance and resulting high sensitivity, the radiationdetectors can replace proportional counters which use multiplicationwithin the gas.

This concept can also replace passive detectors, such as film orthermoluminescent detector material, in applications or apparatus whereimmediate readout would be advantageous. This includes but is notlimited to radon monitoring and occupational monitoring.

What is claimed is:
 1. A radiation detection system for measuringradiation, the system comprising:a radiation detector having at leastone radiation detection subassembly including:means for defining avolume of gas, said gas being a detection medium adapted to be ionizedby said radiation; a surface element positioned in direct contact withsaid gas and being part of said means for defining a volume of gas;means for generating an electric field within said volume of gas and forcollecting ions present therein including at least one collectingelectrode positioned on said surface element for collecting ions createdin said ionizable gas; amplifying means electrically connected to saidcollecting electrode for generating a signal representative of thecollected ions; controlled discharge means for removing charge from saidcollecting electrode; and means for minimizing inaccuracies in saidsystem due to leakage currents to said collecting electrode from saiddischarge means or said amplifying means; interface means for bufferingsaid signal generated by said amplifying means; detector control meansfor controlling said controlled discharge means; and means for supplyingpower to said at least one radiation detection subassembly and saiddetector control means.
 2. The system of claim 1, wherein an input tosaid amplifying means at said collecting electrode is sealed within thevolume of gas and isolated from moisture, and wherein said collectingelectrode is electrically isolated from elements outside of said volumeof gas.
 3. The system of claim 1, wherein said controlled dischargemeans comprises a transistor that unintentionally introduces a leakagecurrent into the collecting electrode, said leakage current beingcontrolled by said means for minimizing inaccuracies.
 4. The system ofclaim 3, wherein said means for minimizing inaccuracies comprises acurrent source for inducing current of a polarity opposite to that ofthe leakage current flowing to the collecting electrode, said currentsource being controlled by said detector control means.
 5. The system ofclaim 4, and further comprising a duplicate controlled discharge meansand a duplicate amplifying means, said duplicate amplifying means andsaid duplicate controlled discharge means being not connected to saidcollecting electrode, and supplying electrical signal information tosaid detector control means for controlling said current source.
 6. Thesystem of claim 1, and further comprising a duplicate controlleddischarge means and a duplicate amplifying means, said duplicateamplifying means and said duplicate controlled discharge means being notconnected to said collecting electrode, and producing an output signalfed to said detector control means for minimizing inaccuracies due toleakage current.
 7. The system of claim 1, wherein said controlleddischarge means removes charge from said collecting electrode inpredetermined size packets of charge, said controlled discharge mansproducing as output a pulse for each packet of charge removed from saidcollecting electrode so that the number of pulses produced as output bysaid controlled discharge means is a measure of the charge collected onsaid collecting electrode, and the rate of said pulses is related to thecurrent to the collecting electrode.
 8. The system of claim 7, andfurther comprising a voltage source, and wherein said controlleddischarge means comprises two transistors connected in series betweensaid collecting electrode and said voltage source, said transistorsbeing controlled and switched sequentially so that only one transistorconducts at any one instant in time for removing predetermined sizepackets of charge from the collecting electrode and delivering saidcharge to said voltage source.
 9. The system of claim 7, and furthercomprising counting means forming a part of said detector control meansfor counting events corresponding to the removal of charge by saidcontrolled discharge means, and wherein said means for minimizinginaccuracies comprises means for controlling said counting means toignore charge removal events if said charge removal events do not occurmore frequently than a predetermined frequency.
 10. The system of claim1, wherein said means for minimizing inaccuracies comprises means fornot permanently electrically connecting said controlled discharge meansto said collecting electrode under control of said detector controlmeans.
 11. The system of claim 10, wherein said controlled dischargemeans uses induced conductivity in the detection medium for controlleddischarge.
 12. The system of claim 10, wherein said controlled dischargemeans uses induced conductivity in the detection medium for controlleddischarge, said conductivity being induced by the radiation beingmeasured.
 13. The system of claim 12, wherein said detector controlmeans includes means for sensing successive accumulations of charge onthe collecting electrode and said controlled discharge means isconnected to the means for supplying power for reversing the polarity ofsaid electric field within said volume of gas for attracting charges ofone polarity to said collecting electrode, and then attracting chargesof a polarity, opposite to said first polarity, to said collectingelectrode.
 14. The system of claim 13, wherein said detector controlmeans controls said controlled discharge means so that measurements canbe made while said electric field is of either polarity.
 15. The systemof claim 1, and further comprising means within the detector controlmeans for enabling measurement of radiation over a total dose rate rangethat extends beyond the range of any single unmodified radiationdetection subassembly.
 16. The system of claim 15, wherein said detectorcontrol means includes selecting means to select a particular radiationdetection subassembly for measuring radiation within its predeterminedaccurate dose rate range.
 17. The system of claim 15, wherein saiddetector control means selects a signal representative of the collectedcharge on one of several collecting electrodes from within a radiationdetection subassembly.
 18. The system of claim 1, wherein said radiationdetection subassembly is capable of sensing charge or current, andfurther includes means for generating a numeric representation of thecollected charge or current, accumulating means for accumulating anumeric representation of the sensed charge or current, andcommunicating means for communicating said numeric representation uponcommand of said detector control means, or in accordance with programmedinstructions.
 19. The system of claim 18, and further including meansfor storing numeric information used in the operation and accumulationof said numeric representation of said sensed charge or current.
 20. Thesystem of claim 19, and further comprising error detection andcorrection means for minimizing errors in communication of said numericrepresentation of said sensed charge or current.
 21. The system of claim11, and further comprising an integrated circuit; wherein saidamplifying means includes at least one input transistor mounted on saidintegrated circuit; and wherein said integrated circuit is located inclose proximity to said collecting electrode.
 22. The system of claim21, wherein an input to said amplifying means at said collectingelectrode is sealed within the volume of gas and isolated from moisture,and wherein said collecting electrode is electrically isolated fromelements outside of said volume of gas.
 23. The system of claim 22,wherein said controlled discharge means comprises a transistor thatunintentionally introduces a leakage current into the collectingelectrode, said leakage current being controlled by said means forminimizing inaccuracies.
 24. The system of claim 23, wherein said meansfor minimizing inaccuracies comprises a current source for inducingcurrent of a polarity opposite to that of the leakage current flowing tothe collecting electrode, said current source being controlled by saiddetector control means.
 25. The system of claim 24, an d furthercomprising a duplicate controlled discharge means and a duplicateamplifying means, said duplicate amplifying means and said duplicatecontrolled discharge means being not connected to said collectingelectrode, and supplying electrical signal information to said detectorcontrol mans for controlling said current source.
 26. The system ofclaim 21, and further comprising a duplicate controlled discharge meansand a duplicate amplifying means, said duplicate amplifying means andsaid duplicate controlled discharge means being not connected to saidcollecting electrode, and producing an output signal fed to saiddetector control means for minimizing inaccuracies due to leakagecurrent.
 27. The system of claim 21, wherein said controlled dischargemeans removes charge from said collecting electrode in predeterminedsize packets of charge, said controlled discharge means producing asoutput a pulse for each packet of charge removed from said collectingelectrode so that the number of pulses produced as output by saidcontrolled discharge mans is a measure of the charge collected on saidcollecting electrode, and the rate of said pulses is related to thecurrent to the collecting electrode.
 28. The system of claim 27, andfurther comprising a voltage source, and wherein said controlleddischarge means comprises two transistors connected in series betweensaid collecting electrode and said voltage source, said transistorsbeing controlled and switched sequentially so that only one transistorconducts at any one instant in time for removing predetermined sizepackets of charge from the collecting electrode and delivering saidcharge to said voltage source.
 29. The system of claim 27, and furthercomprising counting means forming a part of said detector control meansfor counting events corresponding to the removal of charge by saidcontrolled discharge means, and wherein said means for minimizinginaccuracies comprises means for controlling said counting means toignore charge removal events if said charge removal events do not occurmore frequently than a predetermined frequency.
 30. The system of claim21, wherein said means for minimizing inaccuracies comprises means fornot permanently electrically connecting said controlled discharge meansto said collecting electrode under control of said detector controlmeans.
 31. The system of claim 30, wherein said controlled dischargemeans uses induced conductivity in the detection medium for controlleddischarge.
 32. The system of claim 30, wherein said controlled dischargemeans uses induced conductivity in the detection medium for controlleddischarge, said conductivity being induced by the radiation beingmeasured.
 33. The system of claim 32, wherein said detector controlmeans includes means for sensing successive accumulations of charge onthe collecting electrode and said controlled discharge means isconnected to the means for supplying power for reversing the polarity ofsaid electric field within said volume of gas for attracting charges ofone polarity to said collecting electrode, and then attracting chargesof a polarity, opposite to said first polarity, to said collectingelectrode.
 34. The system of claim 33, wherein said detector controlmeans controls said controlled discharge means so that measurements canbe made while said electric field is of either polarity.
 35. The systemof claim 21, and further comprising means within the detector controlmeans for enabling measurement of radiation over a total dose rate rangethat extends beyond the range of any single unmodified radiationdetection subassembly.
 36. The system of claim 35, wherein said detectorcontrol means includes selecting means to select a particular radiationdetection subassembly for measuring radiation within its predeterminedaccurate dose rate range.
 37. The system of claim 35, wherein saiddetector control means selects a signal representative of the collectedcharge on one of several collecting electrodes from within a radiationdetection subassembly.
 38. The system of claim 21, and furthercomprising a guard ring mounted on the surface of said integratedcircuit, said guard ring being kept at the same potential as saidcollecting electrode to intercept leakage current to said collectingelectrode.
 39. The system of claim 38, wherein said guard ring is sizedto minimize induction of voltage onto said collecting electrode due tothe presence of nearby conductive material on said integrated circuit.40. The system of claim 38, and further comprising a capacitor formed onthe integrated circuit connected to the gate of said input transistorfor controllably changing the voltage of the gate without inducing aleakage current.
 41. The system of claim 21, wherein said radiationdetection subassembly is capable of sensing charge or current, andfurther includes means for generating a numeric representation of thecollected charge or current, accumulating means for accumulating anumeric representation of the sensed charge or current, andcommunicating means for communicating said numeric representation uponcommand of said detector control means, or in accordance with programmedinstructions.
 42. The system of claim 41, and further including meansfor storing numeric information used in the operation and accumulationof said numeric representation of said sensed charge or current.
 43. Thesystem of claim 42, and further comprising error detection andcorrection means for minimizing errors in communication of said numericrepresentation of said sensed charge or current.
 44. The system of claim1, and further comprising an unpackaged integrated circuit; wherein saidsurface element in mounted on said unpackaged integrated circuit; andwherein said amplifying means includes an input transistor mounted onsaid integrated circuit.
 45. The system of claim 44, wherein an input tosaid amplifying means at said collecting electrode is sealed within thevolume of gas and isolated from moisture, and said collecting electrodeis electrically isolated from elements outside of said volume of gas.46. The system of claim 44, wherein said controlled discharge meanscomprises a transistor that unintentionally introduces a leakage currentinto the collecting electrode, said leakage current being controlled bysaid means for minimizing inaccuracies.
 47. The system of claim 46,wherein said means for minimizing inaccuracies comprises a currentsource for inducing current of opposite polarity than the leakagecurrent to flow to the collecting electrode, said current source beingcontrolled by the detector control means.
 48. The system of claim 47,and further comprising a duplicate controlled discharge means and aduplicate amplifying means, said duplicate amplifying means and saidduplicate controlled discharge means not being connected to saidcollecting electrode, said duplicate controlled discharge means andduplicate amplifying means supplying electrical signal information tosaid detector control mans for controlling said current source.
 49. Thesystem of claim 44, and further comprising a duplicate controlleddischarge means and a duplicate amplifying means, said duplicateamplifying means and said duplicate controlled discharge being notconnected to said collecting electrode, and producing an output signalfed to said detector controller means for minimizing inaccuracies due tothe leakage current.
 50. The system of claim 44, wherein said controlleddischarge means removes charge from said collecting electrode inpredetermined size packets of charge, said controlled discharge meansproducing as output a pulse for each packet of charge removed from saidcollecting electrode so that the number of pulses produced as output bysaid controlled discharge means is a measure of the charge collected onsaid collecting electrode, and the rate of said pulses is related to thecurrent to the collecting electrode.
 51. The system of claim 50, andfurther comprising a voltage source; and wherein said controlleddischarge means comprises two transistors connected in series betweensaid collecting electrode and said voltage source, said transistorsbeing controlled and switched sequentially so that only one transistorconducts at any one instant in time for removing predetermined sizepackets of charge from the collecting electrode and delivering saidcharge to said voltage source.
 52. The system of claim 50, and furthercomprising counting means forming a part of said detector control meansfor counting events corresponding to the removal of charge by saidcontrolled discharge means, and wherein said means for minimizinginaccuracies comprises means for controlling said counting means toignore charge removal events if said charge removal events do not occurgreater than a predetermined frequency.
 53. The system of claim 44,wherein said means for minimizing inaccuracies comprises means for notpermanently electrically connecting said controlled discharge means tosaid collecting electrode under control of said detector control means.54. The system of claim 53, wherein said controlled discharge means usesinduced conductivity in the detection medium for controlled discharge.55. The system of claim 53, wherein said controlled discharge means usesinduced conductivity in the detection medium for controlled discharge,said conductivity being induced by the radiation being measured.
 56. Thesystem of claim 55, wherein said detector control means includes meansfor sensing successive accumulations of charge on the collectingelectrode and said controlled discharge means is connected to the meansfor supplying power for reversing the polarity of said electric fieldwithin said volume of gas for attracting charges of one polarity to saidcollecting electrode, and then attracting charges of a polarity,opposite to said first polarity, to said collecting electrode.
 57. Thesystem of claim 56, wherein said detector control mans controls saidcontrolled discharge means so that measurements can be made while saidelectric field is of either polarity.
 58. The system of claim 44, andfurther comprising means within the detector control means for enablingmeasurement of radiation over a total dose rate range that extendsbeyond the range of any single unmodified radiation detectionsubassembly.
 59. The system of claim 58, wherein said detector controlmeans includes selecting means to select a particular radiationdetection subassembly for measuring radiation within its predeterminedaccurate dose rate range.
 60. The system of claim 58, wherein saiddetector control means selects a signal representative of the collectedcharge on one of several collecting electrode from within a radiationdetection subassembly.
 61. The system of claim 44, and furthercomprising a guard ring mounted on the surface of said integratedcircuit, said guard ring being kept at the same potential as saidcollecting electrode to intercept leakage current to said collectingelectrode.
 62. The system of claim 61, wherein said guard ring is sizedto minimize induction of voltage onto said collecting electrode due tothe presence of nearby conductive material on said integrated circuit.63. The system of claim 61, and further comprising a capacitor formed onthe integrated circuit connected to the gate of said input transistorfor controllably changing the voltage of the gate without inducing aleakage current.
 64. The system of claim 44, wherein said radiationdetection subassembly is capable of sensing charge or current, andfurther includes means for generating a numeric representation of thecollected charge or current, accumulating means for accumulating anumeric representation of the sensed charge or current, andcommunicating means for communicating said numeric representation uponcommand of said detector control means, or in accordance with programmedinstructions.
 65. The system of claim 64, and further including meansfor storing numeric information used in the operation and accumulationof said numeric representation of said sensed charge or current.
 66. Thesystem of claim 65, and further comprising error detection andcorrection means for minimizing errors in communication of said numericrepresentation of said sensed charge or current.